Facebook's stock is soaring after the social networking company reported stronger-than-expected results for the fourth quarter, fuelled by strong mobile advertising revenue.

Facebook, which turns 10 next week, said that more than half of its advertising revenue now comes from mobile.

That's a big milestone considering it only started showing mobile ads in 2012. Investors fretted at the time that it wouldn't be able to evolve into a "mobile-first" company. The quarter's results are a sign that it has.

At the end of 2013, more than three-quarters of Facebook's 1.23 billion users - 945 million - logged in using their mobile devices at least once a month.

Facebook's stock is up 8.77 dollars, or 16%, to 62.30 dollars in midday trading in New York. It hit a record high of 62.44 dollars earlier.